In manufacturing a semiconductor device, there is a case in which a deep hole is formed in a silicon oxide film by plasma etching. An example of such a semiconductor device includes a dynamic random access memory.
In addition, as semiconductor devices are highly integrated, an aspect ratio of a hole formed in a silicon oxide film is gradually increased. U.S. Pat. No. 7,977,390 discloses a method of achieving such a high aspect ratio. In this method, a step of depositing a protective film containing silicon on side walls of a mask and a silicon oxide film, and a step of etching the silicon oxide film are repeated alternately. The method enables formation of a deep hole by depositing the protective film to protect the mask.